International Journal of Engineering Trends and Technology (IJETT) – Volume 10 Number 7 - Apr 2014
Multi-Path Routing and Wavelength Assignment (RWA) Algorithm for
WDM Based Optical Networks
P. Sakthivel1, P. Krishna Sankar2
1
Final year M.E (CSE), 2Assistant Professor
Department of Computer Science and Engineering
K S R Institute for Engineering and Technology
Tiruchengode, Tamilnadu, India
Abstract- In optical WDM networks, transmission of
information along optical lines is advantageous since it
has high transmission capacity, scalability, feasibility and
also high reliability. But large amount of information is
being carried; any problem during transmission can lead
to severe damage to the data being carried. Hence it is
essential to consider the routing as well as the wavelength
assignment problems and then develop a combined
solution for both the problems. In this paper, we propose
to develop a routing and wavelength assignment algorithm
for selecting the suitable alternate path for the data
packets transmission. Two stages are based on the
available bandwidth and the number of wavelength used
in the link as construction of alternate paths, route and
wavelength selection. In proposed work, Adaptive Routing
and First-Fit Wavelength Assignment (AR-FFWA)
algorithm to be used. For each pair of source and
destination, the path with the minimum granularity values
are selected as the primary path for data transmission,
allocating the sufficient wavelength and the performances
will be evaluated by using ns-2 simulation models. When
we compared to existing system the overall blocking
probability will be reduced to too low.
Keywords-
Wavelength
Assignment,
Blocking
probability, Optical WDM networks, AR-FFWA.



Fully photonic network where fiber amplifiers are
used
Several channels are transmitted simultaneously in
each fiber
The network forms a wide backbone-network
Optical networks employing wavelength division
multiplexing (WDM) offer the promise of meeting the high
bandwidth requirements of emerging communication
applications, by dividing the huge transmission bandwidth
of an optical fiber (~50 terabits per second) into multiple
communication channels with bandwidths (~10 gigabits per
second) compatible with the electronic processing speeds of
the end users.
A. Wavelength Division Multiplexing (WDM)
Optical wavelength division multiplexing (WDM)
networking is being recognized as an efficient technique for
upcoming wide area network environments, because of its
impending ability to meet the increasing demands of low
latency communication and high bandwidth [2]. WDM
allows several signals to be carried independently along the
same fiber provided each signal uses a different wavelength.
As a result same fiber can be shared by many connections.
B. Advantages of Optical Networks
I.
INTRODUCTION
The basic property of single mode optical fiber is its
enormous low-loss bandwidth of several tens of Terahertz.
However, due to dispersive effects and limitations in optical
device technology, single channel transmission is limited to
only a small fraction of the fiber capacity [1]. To take full
advantage of the potential of fiber, the use of wavelength
division multiplexing (WDM) technology has become the
option of choice. With WDM, a number of distinct
wavelengths are used to implement separate channels. An
optical fiber can carry several channels in parallel, each on a
particular wavelength. The number of wavelengths that each
fiber can carry simultaneously is limited by the physical
characteristics of the fiber and the state of the optical
technology used to combine these wavelengths onto the
fiber and isolate them off the fiber. With currently available
commercial technology, a few tens of wavelengths can be
supported within the low-loss. The main characteristics of
WDM can concisely be summarized as follows:
ISSN: 2231-5381





Optical fiber Networks have high capacity
Restoration done in optical layer is faster and
efficient
Optical signals can be transferred as long distance
Wide Bandwidth
Light Weight, Small Diameter
There are three different types of wavelength division
multiplexing:



WDM (Wavelength Division Multiplexing)
CWDM
(Coarse
Wavelength
Division
Multiplexing)
DWDM
(Dense
Wavelength
Division
Multiplexing)
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International Journal of Engineering Trends and Technology (IJETT) – Volume 10 Number 7 - Apr 2014
Fig. 1. Wavelength division multiplexing
Fig. 1 will shows how the wavelength will be assigned to
the each path of the channels and each wavelength is like a
separate channel (fiber).
3) Adaptive routing: In adaptive routing, the route from a
source node to a destination node is chosen dynamically,
depending on the network state. The network state is
determined by the set of all connections that are currently in
progress. One form of adaptive routing is adaptive shortest
cost path routing. For the network in Figure 2, if the links
(1,2) and (4,2) in the network are busy, then the adaptive
routing algorithm can still establish a connection between
Nodes 0 and 2, while both the fixed routing protocol and the
fixed-alternate routing protocols with fixed and alternate
paths would block the connection.
C. Routing and Wavelength Assignment (RWA)
The routing and wavelength assignment problem is an
optical networking problem with the goal of maximizing the
number of optical connections [3]. Each connection request
must be given a route and wavelength. The wavelength must
be consistent for the entire path, unless the usage of
wavelength converters is assumed. Two connections
requests can share the same optical link, provided a different
wavelength is used [4].
D. Routing
Fig. 2. Adaptive routing
Fig. 2 will shows how the adaptive routing will
selects the suitable path.
E. Wavelength Assignment Algorithm
1) Fixed Routing: In fixed routing, a single fixed route is
predetermined for each source-destination pair. When a
connection request arrives, the network will attempt to
establish a light-path along the fixed route. If no common
wavelength is available on every link in the route, then the
connection will be blocked. A fixed routing approach is
simple to implement; however, it is very limited in terms of
routing options and may lead to a high level of blocking. In
order to minimize the blocking in fixed routing networks,
the predetermined routes need to be selected in a manner
which balances the load evenly across the network links.
Fixed routing schemes do not require the maintenance of
global network state information.
2) Fixed-Alternate Routing: In fixed-alternate routing, each
node in the network is required to maintain a routing table
which contains an ordered list of number of fixed routes to
each destination node. When a connection request arrives,
the source node attempts to establish the connection on each
of the routes from the routing table in sequence, until a route
with a valid wavelength assignment is found. If no available
route is found from the list of alternate routes, then
connection request is blocked and lost. In most cases, the
routing tables at each node are ordered by the number of
fiber link segments (hops) to the destination. Therefore, the
shortest path to the destination is the first route in the
routing table. When there are ties in the distance between
different routes, one route may be selected at random.
Another advantage of fixed-alternate routing is that it can
significantly reduce the connection blocking probability
compared to fixed routing.
ISSN: 2231-5381
In routing there are two ways to use the wavelength. In
First case, we can use the same wavelength throughout the
path which spans from source to destination [5]. In the
second case, we are allowed to use different wavelengths in
the path running from source to destination. Among
possible others, few independent wavelength assignment
algorithms are,




Random (R) wavelength assignment
First-Fit (FF) assignment
Most-used (MU) assignment
Least-Used (LU)
II. EXISTING SYSTEM
The O-OFDM networks are only using the Single path
routing so the overall bandwidth blocking probability will
high [9]. If congestion occurs in between routing path that
data could be discard from the transmission process [10].
Here more data loss, more blocking probability and low
through put. An O-OFDM network are using Single Path
Routing and Breadth-First Path Search (BFPS) algorithm
used. The Single-path routing can causes unbalanced traffic
distributions, When Traffic load is high, difficulty to find a
single path routing algorithm [11] [12].
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International Journal of Engineering Trends and Technology (IJETT) – Volume 10 Number 7 - Apr 2014
A. Worst Case of Existing System
IV. SYSTEM FLOW DIAGRAMS
Fig. 4 will shows the system flows of proposed works.
Fig. 3. Fixed Path Routing in Existing System
Fig. 3 will shows fixed path routing for the source node
‘s’ to destination node ‘d’ and here the Bandwidth (BW)
allocation as BW=2 and BW=3 for entire transmission only
the fixed route will be used.
III. PROPOSED SYSTEM
The dynamic routing processes of optical networks are
implemented for these proposed systems [13]. It will be
implemented by using RWA algorithm for selecting route
and wavelength assignments and RMSA with HSMR
algorithm to be used for reducing the bandwidth blocking
probability [14]. The previous Optical system to be
considering the static path transmission but now it will
propose and develop this dynamic path routing and
wavelength assignment algorithm for WDM Optical
network. It is increase the Throughput, reduces the
blocking probability and time delay. The Adaptive routing
path approach to be used in proposed system. Alternate
path routing assumes that every node stores the first N
shortest and predetermined paths to each destination by
utilizing global and local node link information.
Congestion is determined in part by the number of
wavelengths available per path or link. It is fully dynamic
one; those are realized in simulation results.
This proposed work, a route between a sender node and
receiver node is selected from a set of Pre-defined alternate
routes. If any collision occurs in the routed path that time
the data will be path changed and transmit alternate path
from source to destination [15]. Multi-Path routing provides
increased throughput and utilizes the network resources
more efficiently. In the proposed work, a route between a
sender node and a receiver node is selected from a set of
pre-defined routes which are link-disjoint paths, i.e., paths
which do not share a link, and a wavelength is selected
along the selected route [16]. Then the proposed work
selects a route among pre-defined paths and assigns
wavelengths to segments along the selected route in such a
way as to avoid the generation of bottleneck links and the
depletion of a specific wavelength. In this case, further
light-paths cannot be established in the link. Therefore, it
expects to reduce the blocking probability by avoiding the
generation of bottleneck links. In order to distribute loads
and avoid the generation of bottleneck links, the proposed
scheme preferentially selects a route which has segments
with many available wavelengths [17] [18].
Fig. 4. System flow diagrams of Optical networks
Figure 4 has shown the modulated optical signals with
data to be transmitted through optical fiber, here the RWA
algorithm an Adaptive routing and First-Fit wavelength to
be assigned to each path of the networks. Finally, light-path
should be established by using RMSA with HSMR
(OPC/FPS) algorithm and then the data to be transmitted in
different routes [19]. If the congestion will occurs in light
path immediately alternate path should be assigned for the
congested path. Then the performances are evaluated using
NSFNET topology for the simulations [20].
V. SIMULATION RESULTS
In this paper, we are using Network Simulator (ns2) for
simulating the proposed Adaptive Routing and First-Fit
Wavelength Assignment (AR-FFWA) algorithm for
performance evaluation [6] [7] [8]. This will reduce the
overall blocking probability and increasing the throughput.
A. Simulation Modules
1.
2.
3.
4.
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Data packets will be sent to the destination node by
the source node.
The possibility of occurrence of congestion in the
transmission route.
The Alternate Path (backup path) will be choosing
and the traffic will be routed through backup path
to avoid collision.
Performance Analysis
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International Journal of Engineering Trends and Technology (IJETT) – Volume 10 Number 7 - Apr 2014
TABLE I
PARAMETERS USED IN DIFFERENT NETWORK TOPOLOGY
DESIGN
Traffic Loads (Erlangs)
Total costs of the Path
8 node Network topology
Granularity =1
300
9
400
12
500
11
Granularity =2
Fig. 6. Destination node can send the request to the Source node via the
Routers
100
11
200
12
12 node Network topology
Granularity =3
700
26
800
18
900
31
14 node Network topology
Granularity =3
Fig. 7. Packet Template messages to be send to the destination node
Fig. 8. Congested node can be identified in the transmission route and data
can be transmitted via the alternate paths
500
9
600
32
700
37
Table 1. Will explains that different traffic loads (Erlangs)
with total cost of the different paths and below the graph
models can explain simulation results.
Fig. 9. Distribution of the path-distance requests to the different
paths and traffic loads with granularity=1 in 8 node network topology
Fig. 6, 7 and 8 can shows the data transmission,
congestion identification with the alternate path selection.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 10 Number 7 - Apr 2014
Fig. 10. Distribution of the path-distance requests to the different
paths and traffic loads with granularity=2 in 8 node network topology
VI. CONCLUSIONS
This paper proposed a dynamic RWA scheme for WDM
optical networks with routing and wavelength assignment
algorithm. The route and wavelengths are selected for each
light-path based on wavelength availability, Adaptive
Routing and First-Fit Wavelength Assignment (AR-FFWA)
algorithm to be used. In order to establish an efficient path
for a given source and destination pair, initially the
bandwidth and delay will be calculated for every link which
can form a path between the given node pair. Incase if the
link is completely loaded then, it will not be further
considered, incase if it not completely loaded and has free
channels for wavelength assignment then it is further
considered for the formation of the path. Next the shortest
and low traffic path is calculated based on assigning
minimum granularity values. Furthermore, it will
demonstrated the robustness of the projected scheme against
system parameter values such as the number of wavelengths
supported by each fiber and the number of fibers in each
link. Finally this proposed work developed the dynamical
RWA algorithm for optical networks for fast and long
distance
data
transmission.
Through
simulation
experiments, observed that the proposed scheme efficiently
reduces blocking probability in WDM optical networks.
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